Inside they are frighteningly claustrophobic and also hot, with temperatures rising as high as 50°C.

Each team “races” 15.5miles around a track in Lausitz, Germany.

Experts at the annual Shell Eco-Marathon then compare their total fuel economy to calculate the distance each vehicle would be able to travel on just one litre of fuel.

Drivers are selected for being as light as possible and many designs mean they lie down to reduce wind resistance.

The competition is designed to inspire young scientific and engineering talent as well as encourage development of new ways of increasing fuel efficiency and reducing the environmental impact of cars.

More than 40,000 students from 30 nations have taken part since the challenge began a quarter of a century ago.

Cars beetle around the track at an average speed of no less than 18mph during the race.

Some engines are turned on and off, with the cars coasting for as far as they can to increase fuel efficiency.

The bodywork is feather light, often constructed out of carbon or glass fibre, while the engines and wheels vary widely — with many teams opting to use bike wheels for simplicity.

But not all the entrants follow the same design rules.

This year London’s Brunel University decided to dispense with aero-dynamic design in favour of a glass fibre shape which seemed to have been inspired by a milk float.

After rounding the first corner it mysterious disappeared from the track for some running repairs.

The uni came last in the Urban Concept category.

The event attracts eccentric ideas, as a team from Coventry proved by using an engine built from a garden strimmer.

They finished 86th out of 91 teams in the prototype category, managing 486 miles per gallon.

The other Brit representatives, from the University Of Central Lancashire, finished 87th with 460mpg.

Not everyone takes it too seriously, one vehicle was designed to look like a giant condom.

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But, after three intense days the most successful team was St Joseph La Joliverie from Nantes, in France, in their car Microjoule.

Their prototype internal-combustion car proves it is capable of covering an astonishing 2,343 miles or 3,771km on a single litre of petrol.

That equates to 10,651 miles to the gallon — the distance between London and Sydney, Australia, half way round the world.

But even that fails to beat the world record set by a Swiss team of 2,384 miles in 2005.

With that kind of fuel efficiency it is no surprise big car companies take a close interest in the budding young designers, who are all aged between 16 and 26.

Brilliant and innovative as they are, it will take a while to come up with an estate model to carry two children, luggage, bikes and a dog in the back.